Primary pulmonary hypertension (PPH) is a rare disease of unknown etiology characterized by severe, isolated pulmonary arterial hypertension leading to right ventricular failure and death. Genetic studies in patients with Familial PPH (FPPH) indicate that the majority carry mutations in the BMP Type II receptor (BMPR2) locus, while functional assays indicate that defects in BMP-signaling are also found in patients with sporadic PPH. For this reason, analysis of cellular dysfunction in FPPH patients carrying defined BMPR2 mutations provides an opportunity to explore pathological events underlying both sporadic and familial forms of PPH. Despite this, the cellular defects resulting from these mutations are essentially unknown, as direct approaches to evaluate alterations in cell function have been hindered by limited access to FPPH patient derived vascular cells. To address this we have developed a surrogate system using primary skin fibroblasts from patients with FPPH to study effects of diverse BMPR2 mutations on cellular function. These cells are easy to harvest and propagate, and share properties in common with vascular smooth muscle cells. Skin fibroblasts and pulmonary artery smooth muscle cells from patients with FPPH do not proliferate in response to BMPs, and show constitutive phosphorylation of the TGF-beta-activated Smads. These findings are the first evidence of a consistent abnormality associated with diverse BMPR2 mutations. In these studies we will validate this cell culture system by interrogating the functional impact of this defect in Smad-signaling using FPPH fibroblasts and pulmonary artery smooth muscle cells. We will then use these to evaluate an unbiased approach to identify changes in the cellular proteome shared by FPPH cells carrying a range of different BMPR2 mutations. These studies will establish a technological platform to identify and evaluate cellular abnormalities in these patients and in patients with other forms of pulmonary arterial hypertension.